Electroacoustic binaural listening system



Jan 29 1946 F. s. cLAAssEN 2,393,885

ELECTRO-ACOUSTIC BINAURAL LISTENING SYSTEM Filed nec. 2s, 1944 Fllli'l- M /N veA/rca? Arm/QNQX l Frederic' s. ommen, Bei-genaue, N. J., assigner to the Government of the United States of America, as represented by the Secretary of .application December 2a, 1944, sena! No. 569,548

' 5 Claims.

f The invention describedv herein may be manufactured and used by or for the Government for governmental purposes, without the payment ofany royalty thereon.

This invention relates to improvements in elec- I tro-acoustic binaural listening systems. l

A binaural listening system of the type herein considered comprises two transmission channels,

each of which ls composed of a sound pick-up or microphone, an amplifier, a wire transmission line, and a, sound reproducer or receiver. The microphones of the two channels are mounted together so that their spacing with respect to each other is approximately that of the ears of a human. The receivers of the two channels are mounted asV a pair of head receivers, individually connectedlto their corresponding channels. If the overall characteristics of the two channels are the same, they will pick up a sound with the same phase, intensity and arrival time relationship between them as would the human ears and transmit the sound to the receivers with the same relationships. The system enables the quality, the approximate direction and the character of sounds to be heard by a person located at some distance from the point at which actual listening is desired just as though the person were actually at the listening point. In such a system, however, besides matching the components of the two channels, in order to provide similar trans-l ynovel arrangements and circuits hereinafter described and illustrated in the accompanying drawing, forming a part hereof and in which:

The figure is a schematic diagram of the electrical circuits and apparatus in accordance with the invention.l

Referring to the drawing. the binaural listening 'system is shown to comprise t'wo similar channels. each of which has a listening microphone Il', a transformer I2 coupled to a three stage resistance coupled amplifier with degenerative' feedback around all three stages. The output of the amplifier is connected through an impedance vmatching transformer i3 to a wire transmission line, which is terminated in an impedance matching transformer I4 connected to a head receiver il.

-One of the channels has variable resistance means IB for adjusting the feedback voltage fed to the screen of the first vacuum tube to control the gain of that channel. 'I'he other channel has a fixed feedback. The output of both channels is controlled simultaneously by a dual potentiometer unit i8 in the grid circuitr of the first tube. 'I'he amplifier output transformer i3, the wire line and the receiver impedance matching transformer il are phantomed to provide a circuit for telephonie communication between the two ends microphones will result in opposing voltages atI the amplifier, and ii.' the gains of the amplifiers are equal, the resultant voltage will be zero; Therefore, by listening on the head receivers to a sound being picked up by the microphones, and adjusting the gain of one amplifier until a minimum of sound is heard, the equality of gain in the two channels is established.v

It is desirable that means be provided for determining quickly and Without auxiliary equipment that the lines connecting the outpostl unit with, the sound control unit have been correctly Doled: that is, that no transposition has been introduced in the connection between these units which would have the effect of reversing the relaln position 2, designated Pole, and switch S4.,

Ss on position 1, designated Pole, the inputs to the twov amplifiers are connected in parallel l vand the output voltages of the two receiver impedance matching transformers are connected voltages at the receivers.

together in series with a. pair of head receivers so that the voltages' oppose each other when the lines are poled properly. With this connection, providing the amplier gains have been previously equalized, any sound picked up by the microphones will result in equal and opposing Therefore, by listeningon the head receivers to a sound being picked up by the microphones and reversing the connections of the two wires of one channel transmission line| the connection resulting in minimum sound in the receivers is the connection for proper poling of the transmission line.

When the wafer switch S1, Sa, Ss is turned to position 3, designated Listen and the toggle switch S4, S5 is operated. to Listenl the signals in the two channels are isolated from each other and the system is in condition for binnural listening.

From the above description it will be seen that f there has been provided simple and eiective means for properly poling two wire transmission lines of a binaural listening system.

The above description is to be considered as illustrative and not limitative of the invention,y of which modifications can be made without departing from the scope of the appended claims I claim:

1. In a binaural listening system having two channels, each of said channels including a three stage resistance coupled ampliiier with degenerative feedback, means to adjust the amplifiers of one channel to equalize the gain of the ampliners of the two channels, potentiometer means for varying the gains of both channels simultaneously, wire transmission lines coupled to said channels, head receivers. anda double-pole double-throw reversing switch for connecting the receivers to the tron lines with the proper polarity.

2. In a binaural listening system having two channels. ,each of said channels including a multi-stage resistance coupled amplifier with degenerative feedback, means to adjust the ampliilers of one channel to equalize the gain of the amplifiers of the two channels, wire transmission lines coupled to said channels, receivers, and reversing switching means for connecting the receivers to the transmission lines with the proper polarity.

3. In a binaural listening system having two channels, each ot said channels including a multi-stage ampliiler. means to adjust the ampliner of one channel to equalize the gain of the ampliers of the two channels, wire transmission lines coupled to said channels, receivers, and switching means i'or connecting the receivers to thetransmission lines with the proper polarity.

4. In a binaural listening system having two channels, wire transmission lines coupled to said channels, receivers, and reversing switching means for connecting the receivers to the transmission lines with the proper polarity.

5. In a binaural listening system having two channels, each of said channels including anampliiler, means to adJust the ampliier of one channel to equalize the gain of the amplifiers of the two channels, wire transmission lines coupled` to said channels, receivers, and reversing switching means for connecting the receivers to the transmission lines with the proper polarity. FREDERIC S. CLAASSEN. 

